By way of example, let us consider a YACC program. YACC (Yet Another Compiler-Compiler) is a program generator for generating a syntactic analysis program or a parser as already known in the field of compiler technologies, and a YACC program is one described according to YACC rules. An input YACC command calls the YACC program to be converted into a C language program achieving its function.
Such a YACC program as a source program has conventionally been treated as text data, and its editing work has been carried out by using a text editor, which has caused a difficulty in editing the program structure although it allows the lexical elements to be edited. That is, if the program structure suffers some change, then the need to change the entire program has arisen and a vast amount of labor has been needed for editing it anew. Further, occasionally, it has been necessary to uneconomically recode the entire program from the very beginning.